Life at the extremes

June 20, 2000

Frogs that freeze solid in winter - then thaw out and hop away in the spring. Seals that can dive almost a mile deep. Tiny creatures that relish acid strong enough to eat through your shoe. Does this sound like science fiction? It isn't. All kinds of things thrive under conditions that we humans think are impossible. Here are just a few:

Ancient and extreme

Superman could learn a thing or two from some 3.7 billion-year-old microorganisms. A number of them snack on toxic wastes. Others have no problem swimming in scalding water, or surviving massive doses of radiation.

Harold Schreier, of the University of Maryland's Center of Marine Biotechnology in Baltimore, says these tiny beings are "found in environments we thought would not be habitable." Scientists call them "extremophiles" - creatures that love extremes.

Dr. Schreier notes that many extremophiles belong to an evolutionary classification called Archaea (sometimes called Archaebacteria). Archaea (ar-KAY-yuh) means "ancient."

Of all the microorganisms that live in extreme conditions, the most famous is a pink bacteria. Scientists have nicknamed it "Conan the Bacterium." Its real name is Deinococcus radiodurans.

Scientists find "Conan" living in places where the temperature may reach 212 degrees F. (the boiling point of water), in acid baths (in the stomach of a cow, for instance), and even in storage containers filled with radioactive nuclear waste.

D. radiodurans was discovered back in the 1950s during experiments on sterilizing food using radiation.

After zapping meat with high levels of gamma radiation, researchers were startled to see that this bacteria survived. In fact, it thrived. Now scientists are looking for ways to use the bacteria's remarkable talent to break down nuclear and toxic wastes.

Another extremophile, Methanogenium frigidum, was discovered in 1997. A team led by Prof. Davis Boone of Portland (Ore.) State University found the organism in the icy salt waters of Ace Lake, Antarctica. The creature loves the cold so much that it dies when the temperature gets above 64 degrees F. - a little cooler than room temperature.

Not only that, Methanogenium frigidum is "a strict anaerobe," Boone says. That means it can't live where there is any oxygen. "They live on the table scraps of the microbial world," he adds. They aren't fussy eaters, in other words. In fact, they make their own food using such substances as hydrogen and bicarbonates.

They could be an energy source, because they produce methane gas. The methane reacts with water to form methane hydrates. "There is more energy in methane hydrates than in all the petroleum and gas reservoirs known on earth," he says.

Another extreme-loving tiny creature is Bacillus infernus. It likes hot places - 150 degrees F. hot. It was found in an exploratory well in Virginia, two miles underground. It doesn't need oxygen, but uses iron compounds instead.

Halobacterium salinarum can withstand salt concentrations of up to 30 percent. (Most seawater is only 4 or 5 percent salt.) It lives in the Mideast's Dead Sea, along with some salt-loving plants called halophytes. That's all that can live in the Dead Sea, the saltiest place on earth.

Very warm worms

On the ocean floor along the East Pacific Rise, off the coast of Mexico, the earth's crust is shifting and cracking. From these cracks, 660-degree F. water brimming with what are considered toxic chemicals shoots up like a geyser. When particles (iron and sulfides) fall back down, they create dark, chimneylike structures called "black smokers." This inhospitable setting is home to the Pompeii worm (Alvinella pompejana).

It is one of more than 80 species of marine beard tube worms belonging to the classification Pogonophora. Some scientists believe that outside of bacteria and archaea, the Pompeii worm is the most heat-tolerant creature on earth.

Almost four inches long, the worm looks like a shaggy, whiskered comma trying to hide inside a cylindrical, papery tube. The whiskers aren't real, though. They are actually strings of bacteria.

Fastened to the side of a black smoker chimney, the worms' tubes are subjected to temperatures up to 212 degrees F. Inside the tube, though, it's a balmy 154 to 185 degrees.

Occasionally, the worm ventures a few inches away from its tube, where the water temperature drops rapidly to 72 degrees F. How the worm adapts to a 140-degree drop in temperature confounds scientists. So does its ability to live among all those chemicals considered poisonous. One theory is that somehow the bacteria on its back are a help.

Fast, fiery ants

You may have heard of fire ants, especially if you live in the Southern United States. But have you heard of an ant that can run across fiery hot ground? The Sahara desert ant (Cataglyphis bicolor) is among the most heat-tolerant insects.

It lives in the Sahara, where food is scarce. But this ant has developed a special strategy. It eats dead insects and other small arthropods that have perished in the desert heat.

Other desert insects get their food during the evening or early morning, when temperatures are less than 113 degrees F. But Cataglyphis bicolor boldly goes out in the midday sun, when the ground temperature reaches 140 degrees. So while its predators are hiding in cooler spots, the Sahara ant safely hunts for dinner. It can stay out in the desert heat as long as its body temperature stays below 128 degrees. Otherwise, it may end up like the meals it is hunting.

How does this ant perform its heat-defying feat? First of all, it's speedy - for an insect. One such ant species has been clocked at 39 inches per second. (OK, so it's only 3.1 miles an hour. That's still really fast for an ant.) The hotter the ground, the faster the ant runs.

It also has relatively long legs. Its legs raise it 1/8 to 1/4 inch above the ground. That tiny distance from the soil can mean a temperature drop of 44 degrees.

And when the going gets tough, these creatures play it smart. They take frequent breaks in what scientists call "thermal refuges." We call them "shady spots."

Living frog-sicles

What does a cold-blooded amphibian do when it's cold enough to freeze a pond solid? If you're a toad, you might hibernate in underground rock chambers near streams. That's because running water keeps the temperature just above freezing.

But if you're a wood frog, gray tree frog, spring peeper, or chorus frog, you can just freeze solid and wait for spring.

The wood frog (Rana sylvatica) turns into one of these remarkable "frog-sicles." Wood frogs live in damp woodlands in the Southeastern United States (down to northern Georgia), and in Alaska and parts of Canada. The largest wood frogs are about 3-1/4 inches long. Their croak sounds like a small duck. Most have a dark facial mask, but their coloring ranges from yellowish-brown to pink, brownish-black, and black.

Bob Hay works for Wisconsin's Department of Natural Resources in Madison. He explains how the freezing process works. First, the frogs bury themselves in leaf litter. "When their [body] temperature reaches 32 to 33 degrees F., the body cells become saturated with a glycol-like substance," he says. This substance is equivalent to nature's antifreeze. It keeps the frog's cells from being damaged by freezing.

Scientists have discovered that up to 65 percent of the water in a wood frog's body can freeze. The water freezes outside each cell, but not inside it. Ice crystals inside would cause damage.

After the antifreeze process is complete, the frog's heart stops beating and it stops breathing. All muscle movement halts. The frog appears to be frozen solid.

When spring arrives, the frogs thaw. How the heart starts beating and the lungs start breathing again is still a mystery.

Champion divers

Northern elephant seals (Mirounga angustirostris) were hunted almost to extinction for their pelts in the 1800s. At one point only about 100 of the seals were left. Fortunately, the slaughter ended. In 1999, the National Wildlife Federation estimated the seal's population at 150,000.

These powerful seals are the largest four-flippered marine mammals in the world. What's more, they are also one of the deepest-diving mammals on earth (under earth?). They can withstand enormous underwater pressure.

Sperm whales and several species of beaked whales descend to 3,280 feet or more. But the northern elephant seal beats them all. One seal, tagged No. 666 by the Hubbs-Sea World Research Institute, reached a record depth of 5,150 feet -almost a mile! And not only can they dive deeply, they can stay at such depths for up to an hour.

Northern elephant seals are odd-looking. Males have a trunklike snout. Males and females appear reddish- (or yellowish-) brown in springtime, but after a summer molting become gray-brown. Bull seals are 20 feet long and can weigh two tons. Females are much smaller, weighing less than a ton.

Robert Carney, a professor of oceanography at Louisiana State University in Baton Rouge, calls the deep sea "the largest environment on earth." Here, sunlight fades to darkness and immense pressure builds. To better understand what extreme pressure can do to an object, researchers took a normal-size styrofoam cup to a depth of 2,900 meters (9,512 feet). When the cup was brought back to the surface it was less than half its size! (For a picture, Go to: people.whitman.edu/~yancey/deepsearesearch.html Scroll down to "IV. High Pressure.")

Human divers must take special precautions when they dive deep underwater. Nitrogen in the air they breathe becomes dissolved in their blood and can cause problems. Recreational divers don't go deeper than 130 feet or so.

Yet creatures like the northern elephant seal dive to great depths constantly without ill effect. The way marine mammals' lungs respond to pressure has something to do with it. Dr. Carney says marine creatures have made other unique biochemical adaptations. Scientists hope to learn more about how humans can cope with extreme pressure by studying the northern elephant seal.

Conclusion

Researchers are finding new species in places once thought to be uninhabitable. These amazing - to us - creatures are forcing scientists to expand their definition of what's needed to support life. Who knows? Conan the Bacterium and his extremophile friends may be there to greet human visitors to other planets.